Light fibers are often useful for illuminating an area that is remote from a light source by conducting light through the fiber by total internal reflection. These fibers can be made with varying diameter and length. Light fibers having a diameter of 5 mm or greater are often referred to as "large core optical fibers" and have been used, for example, as accents for architectural features, as lights for areas that would otherwise be hazardous due to the presence of, for example, the heat or electricity present with incandescent or fluorescent lights (e.g., underwater or poolside lights), and as building or vehicle interior lights.
Light can be emitted from light fibers in a number of ways. First, light can be emitted from the end of the light fiber. This type of light emission may be referred to as "end-light". Most light fibers provide at least some "end-light". Many light fibers are designed to maximize internal reflection so that the primary function of the light fiber is to conduct light from a light source to a remote location. The light emitted by this type of light fiber is primarily "end-light".
Second, light can be emitted radially along a portion of or over the entire length of the light fiber. This light is often referred to as "side-light". Most light fibers emit this type of light, which is often due to imperfections in the light fiber, including imperfections in the core and cladding of the light fiber and/or an imperfect interface between the core and cladding. For light fibers which are designed to maximize internal reflection, this type of light emission is minimized; however, there is typically at least some minimal amount of "side-light" which is often seen as a faint glow around the light fiber. The "side-light" is typically a diffuse light.
Light fibers may also be formed which purposefully include mechanisms or structures for extracting light along the length or a portion of the length of the fiber. For example, imperfections in the core or cladding or at the interface between the core and cladding may be introduced to interrupt the internal reflection of at least a portion of the light. Examples of one method for extracting light in this manner are provided in U.S. patent application Ser. No. 08/957,554, entitled "Optical Waveguide with Diffuse Light Extraction", filed Oct. 24, 1997 by David George Freier, Joseph John Bianconi, and Richard Decena Ornelaz, Jr. These light fibers can be used, for example, as visible or decorative articles for providing a ribbon of light along a distance. Light extracted in this manner is typically diffuse.
Another method of extracting light includes redirecting light in a controlled manner out of the light fiber by means of optical elements introduced into the light fiber core or applied directly thereto, such that the function of the light fiber is to conduct light from a source to a specific location other than the end of the fiber. This method of extraction may provide diffuse light; but is more commonly used to produce directed light. Such fibers may be used to provide directed light at particular points or positions, for example, on a screen or other object.
Often, however, it is desirable to provide diffuse light which is directed in a particular set of directions, rather than emanating in all directions. For example, light from a desk lamp is typically diffuse light so that it provides a wide area of illumination. However, the light is preferably directed toward the desk. Diffuse light which is emitted from a light source, such as an incandescent or fluorescent light bulb, in the desk lamp, however, is typically emitted in all directions. This is an inefficient use of the light because not all of the light is properly directed. A significant portion of the light is radiated away from the desired illumination location.
Light fibers can be an efficient way to transmit light and illuminate desired areas using light from a distant light source. However, just as with other light sources, light fibers may not efficiently direct the emitted light, especially if the light is "side-light" or diffusely extracted. There is a need for devices and methods for efficiently directing diffuse light from a light fiber in a set of directions to illuminate a desired area with diffuse light.